This invention relates to game balls, and, more particularly, to a game ball with a spherical core formed from a blend of a foamed mixture of ionomer resins and low density polyethylene.
This invention is an improvement over the game balls described in my prior U.S. Pat. No. 4,861,028. As described in my prior patent, soft balls have historically been made by forming a spherical core of cork, kapok, or similar material which is bound together. A layer of windings of string or yarn is wrapped over the core and a leather cover is placed over the windings and stitched together.
In recent years, game balls, particularly softballs, have been made from molded plastic cores. For example, U.S. Pat. No. 4,149,720 describes a ball which includes a foamed polyurethane core and a leather cover. U.S. Pat. No. 4,364,565 describes a ball which includes a spherical core made from foamed ethylene vinyl acetate copolymer and Surlyn, an ionic copolymer which is available from E. I. DuPont de Nemours and Co. (DuPont) U.S. Pat. No. 4,610,071 describes a ball which includes a core which is molded from Nucrel (ethylene acid copolymer) and filled with polyurethane. A cover is sewn over the core. U.S. Pat. No. 3,069,170 describes a ball which includes a core of foamed polyethylene and a cover. U.S. Pat. No. 4,463,951 describes a ball which is made by rotationally molding an outer layer of foamed polyvinyl chloride and injecting polyurethane foam into the cavity.
The following U. S. Pat. Nos. describe balls which are formed from Surlyn: 4,572,507, 4,529,200, 4,568,083,and 4,653,752.
Specifications for softballs have been issued by two governing organizations, the United States Slow-pitch Softball Association (USSSA) and the Amateur Softball Association (ASA). The specifications of the USSSA in effect before 1989 permitted 11 and 12 inch softballs to have a coefficient of restitution (COR) ranging from 0.44 or under to 0.52, depending upon the category or class in which the ball was used. Different categories would be indicated for example, by the color of the stitching on the cover. Beginning in 1989 the COR of USSSA licensed balls could not exceed 0.50.
Coefficient of restitution (COR) is one measure of the liveliness of the ball. COR is measured by propelling a ball against a hard surface at 60 mph (88 fps) and measuring the rebound speed of the ball. COR is expressed in terms of the ratio of the rebound speed to 60 mph (88 fps).
Other qualities of softballs are important which are not included in the foregoing "official" specifications. These qualities include the sound of the ball when batted, texture of the ball, the "feel off the bat" or, the feel which the batter experiences at the moment of impact, flight distance and consistency, and durability.
My prior U.S. Pat. No. 4,861,028 describes a softball which includes a hollow core which is formed by rotationally molding low density polyethylene or a mixture of low density polyethylene and an ethylene acid copolymer. The specific ethylene acid copolymer described is available from DuPont under the name Nucrel. The low density polyethylene used is sold by the USI Division of Quantum Chemical Corporation under the designation Microthene MN718 and has a density of 0.915 grams/cc and a flexural modulus of 20.6 kpsi (1000 pounds per square inch). The softballs formed in accordance with my prior patent have not been well received. Those softballs did not carry as well as solid core balls, and the hollow balls had a tendency to fracture when played in temperatures below 40.degree. F.